Degree Of Handedness Research Articles

P294 Developmental profile of interhemispheric inhibition in children

Question Interhemispheric inhibition (IHI) is a crossed, transcallosal inhibitory relationship between the left and right motor cortex (M1). This can be assessed in vivo using transcranial magnetic stimulation (TMS). Interhemispheric interactions may be altered in disease such as stroke where IHI imbalance is a potential target for therapeutic neuromodulation. IHI is well defined in adults, but its properties in the developing brain are poorly defined. Methods 24 typically developing, right-handed children aged 6–18 years completed a TMS-evaluation of transcallosal inhibition. Bilateral ipsilateral silent period (iSP) measures delivered suprathreshold (120% resting motor threshold, RMT) stimulation during 50% maximum contraction of the ipsilateral first dorsal interosseous. Bidirectional paired-pulse IHI (LtoR and RtoL) delivered a 120%RMT conditioning stimulus prior to contralateral 120%RMT test stimulus at interstimulus intervals (ISI) of 8, 10, 40 or 50 ms. Results Left iSP latency ( r = −0.38) and suppression ( r = 0.48) correlated with age and degree of handedness ( r = 0.49). Right iSP was not associated with age or handedness. Children exhibited IHI in both LtoR and RtoL directions with maximal reduction of 70% in RtoL at a 40 ms ISI. RtoL IHI was greater than LtoR at ISI of 10, 40 and 50 ms. IHI was positively correlated with handedness in both directions ( r = 0.47): more “right-handed” subjects had less IHI. iSP suppression and LtoR IHI were negatively correlated ( r = −0.53), whereas iSP suppression and RtoL IHI displayed a positive correlation ( r = 0.52). Conclusions Interhemispheric inhibition is measureable in children with TMS. iSP and IHI demonstrate developmental effects of age and laterality. In contrast to some adult descriptions, elements of iSP and IHI appear to be associated. Understanding the developmental profile of IHI and iSP may inform the study of interhemispheric neurophysiology in pediatric disease states.

The contributions of handedness and working memory to episodic memory.

Past studies have independently shown associations of working memory and degree of handedness with episodic memory retrieval. The current study takes a step ahead by examining whether handedness and working memory independently predict episodic memory. In agreement with past studies, there was an inconsistent-handed advantage for episodic memory; however, this advantage was absent for working memory tasks. Furthermore, regression analyses showed handedness, and complex working memory predicted episodic memory performance at different times. Results are discussed in light of theories of episodic memory and hemispheric interaction.

Handedness and schizotypy: The potential effect of changing the writing-hand

Mixed-handedness, which has been associated with schizotypy in recent studies, might exist for at least two different reasons: it is innate or it has been forced. We examined whether the association between mixed-handedness and schizotypy differs depending on its source. We enrolled 3485 college students in Taiwan. We used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess schizotypy, and the Annett Hand Preference Questionnaire to assess handedness. Two ways of classifying handedness were examined: the three-way classification based on Annett's categories and mixed- vs. non-mixed-handedness based on Degree of Handedness. Both mixed-handedness groups showed higher positive schizotypy scores. Among mixed handers, those who had been required to change their writing hand from left to right had higher positive schizotypy scores. Being forced to change writing hand seemed to be related to a higher level of schizotypy. The potential effect of the social pressure against using the left hand for writing is discussed.

The handedness-associated PCSK6 locus spans an intronic promoter regulating novel transcripts.

We recently reported the association of the PCSK6 gene with handedness through a quantitative genome-wide association study (GWAS; P < 0.5 × 10−8) for a relative hand skill measure in individuals with dyslexia. PCSK6 activates Nodal, a morphogen involved in regulating left–right body axis determination. Therefore, the GWAS data suggest that the biology underlying the patterning of structural asymmetries may also contribute to behavioural laterality, e.g. handedness. The association is further supported by an independent study reporting a variable number tandem repeat (VNTR) within the same PCSK6 locus to be associated with degree of handedness in a general population cohort. Here, we have conducted a functional analysis of the PCSK6 locus combining further genetic analysis, in silico predictions and molecular assays. We have shown that the previous GWAS signal was not tagging a VNTR effect, suggesting that the two markers have independent effects. We demonstrated experimentally that one of the top GWAS-associated markers, rs11855145, directly alters the binding site for a nuclear factor. Furthermore, we have shown that the predicted regulatory region adjacent to rs11855415 acts as a bidirectional promoter controlling the expression of novel RNA transcripts. These include both an antisense long non-coding RNA (lncRNA) and a short PCSK6 isoform predicted to be coding. This is the first molecular characterization of a handedness-associated locus that supports the role of common variants in non-coding sequences in influencing complex phenotypes through gene expression regulation.

Need for cognition moderates paranormal beliefs and magical ideation in inconsistent-handers

ABSTRACTA growing literature suggests that degree of handedness predicts gullibility and magical ideation. Inconsistent-handers (people who use their non-dominant hand for at least one common manual activity) report more magical ideation and are more gullible. The current study tested whether this effect is moderated by need for cognition. One hundred eighteen university students completed questionnaires assessing handedness, self-reported paranormal beliefs, and self-reported need for cognition. Handedness (Inconsistent vs. Consistent Right) and Need for Cognition (High vs. Low) were treated as categorical predictors. Both paranormal beliefs and magical ideation served as dependent variable’s in separate analyses. Neither set of tests yielded main effects for handedness or need for cognition. However, there were a significant handedness by need for cognition interactions. Post-hoc comparisons revealed that low, but not high, need for cognition inconsistent-handers reported relatively elevated levels of paranormal belief and magical ideation. A secondary set of tests treating the predictor variables as continuous instead of categorical obtained the same overall pattern.

Handedness and social anxiety: Using Bryden's research as a catalyst to explore the influence of familial sinistrality and degree of handedness

ABSTRACTPhil Bryden's work has impacted on many areas of laterality, including degree and measurement of hand preference, as well as influences of familial sinistrality (FS). For example, Bryden[(1977). Measuring handedness with questionnaires. Neuropsychologia, 15, 617–624] is a well-cited and influential paper that remains relevant to this day. Inspired by this we extended our analysis of the relationship between handedness and anxiety in a number of ways. We used familial handedness and strength of handedness to examine their potential influences on anxiety, and extended our research by exploring their relationship to social anxiety, using the Social Phobia Inventory (SPIN). Inconsistent left-handers (ILH) were found to be more socially anxious. In all categories of SPIN except avoidance, ILH were significantly more anxious than consistent right- and left-handers. There were FS differences between ILH with a first degree left-handed relative (FS+) compared to ILH with no first degree left-handed relative (FS−) on all categories of anxiety scores. Within FS+ participants, ILH had significantly higher anxiety scores, compared with consistent handers across all categories. This suggests that ILH's social anxiety may be influenced by a close left-handed relative. Inspired by examining Bryden's work for this special issue, we will continue to add both strength of preference and familial handedness to our work.

The influence of M. P. Bryden's work on lateralization of motor skill: Is the preferred hand selected for and better at tasks requiring a high degree of skill?

ABSTRACTOne question of interest to Dr M. P. Bryden was how skilled motor behaviour, task complexity, and the degree of handedness are linked. His research suggested that there would be dissociation between hand preference and performance for skilled versus unskilled actions. The thought was that “simple” or unskilled tasks such reaching or grasping could be performed equally well by either hand, and thus either could be selected. Skilled tasks such as fine manipulation would be performed best by the preferred hand and thus it would be selected more frequently. Over the past two decades, researchers have attempted to determine whether such a definition of skilled action best encapsulates the specialization of the preferred hand. The current paper will review M. P. Bryden's research on skilled motor behaviour, as well as more recent work, and explore the question of whether the preferred hand is actually superior and preferred for actions requiring manipulation.

Factor analysis of the Edinburgh Handedness Inventory: Inconsistent handedness yields a two-factor solution

While neuropsychology has long focused on direction (left versus right) of handedness, a growing body of evidence indicates that degree (inconsistent versus consistent) of handedness is at least as important. A promising feature of this new emphasis on degree of handedness is its greater concordance with extant genetic models of handedness, which posit a continuum from inconsistent-handedness to consistent right-handedness, not a continuum from left- to right-handedness. Specifically, departures away from consistent-right-handedness are thought to reflect the action of a neutral genetic factor that leaves handedness up to random environmental influences. To test whether handedness in inconsistent-handers reflects the presence of multiple factors (compared to the presence of a single factor only in consistent-right-handers), factor analyses of handedness inventory scores were conducted on data from 987 right-handers, divided into consistent- versus inconsistent-handers. Consistent with predictions, analyses of inconsistent- versus consistent-handers yielded two versus one factor solutions, respectively. Results are discussed in terms of their potential implications for genetic models of handedness and for researchers interested in consistency of handedness as a neuropsychological variable.

Degree of handedness and priming: further evidence for a distinction between production and identification priming mechanisms.

The distinction between implicit and explicit forms of memory retrieval is long-standing, and important to the extent it reveals how different neural architecture supports different aspects of memory function. Similarly, distinctions have been made between kinds of repetition priming, a form of implicit memory retrieval. This study focuses on the production–identification (ID) priming distinction, which delineates priming tasks involving verification of stimulus features as compared to priming tasks that require use of a cue to guide response retrieval. Studies investigating this dissociation in dementia or similar patient populations indicate that these forms of priming may differ in their neural bases. The current study looks at degree of handedness as a way of investigating inferred neural architecture supporting these two forms of priming. A growing body of research indicates that degree of handedness (consistent, or CH, versus inconsistent, or ICH) is associated with greater interhemispheric interaction and functional access to right hemisphere processing in ICH, with superior performance seen in ICH on memory tasks reliant on this processing. Arguments about the theoretical mechanisms underlying ID and production forms of perceptual priming tasks suggest that performance on these tasks will differ as a function of degree of handedness. We tested this question in a group of CH and ICH young adults, who were asked to study lists of words prior to performing a production priming task (word stem completion, WSC), a perceptual word ID task, and a word stem cued recall task. While both handedness groups exhibited reliable priming across tasks, WSC priming was greater in ICH than CH participants, with ID priming not differing between groups. This dissociation supports the argument that production and ID forms of priming have different underlying neural bases.

Comparing methods for determining motor-hand lateralization based on fTCD signals.

The lateralization index (LI) as determined from functional transcranial Doppler sonography (fTCD) can be used to determine the hemispheric organization of neural activation during a behavioral task. Previous studies have proposed different methods to determine this index, but to our knowledge no studies have compared the performance of these methods. In this study, we compare two established methods with a simpler method proposed here. The aim was to see whether similar results could be achieved with a simpler method and to give an indication of the analysis steps required to determine the LI. A simple unimanual motor task was performed while fTCD was acquired, and the LI determined by each of these methods was compared. In addition, LI determined by each method was related to behavioural output in the form of degree of handedness. The results suggest that although the methods differed in complexity, they yielded similar results when determining the lateralization of motor functions, and its correlation with behavior. Further investigation is needed to expand the conclusions of this preliminary study, however the new method proposed in the paper has great potential as it is much simpler than the more established methods yet yields similar results.

Estimation of heritability for varied indexes of handedness

Inconsistent results of the molecular studies for handedness have been reported. One of the key issues involved could be ways of assessing handedness. The current study aimed to identify the index of handedness better reveal the genetic component, which showed higher heritability. We measured handedness using the Annett's handedness questionnaire. The college students participating in this study filled the questionnaire in the class while their first-degree relatives returned questionnaires one to two weeks later. A total of 1,968 subjects returned their questionnaires, including 640 college students and 1,328 first-degree relatives. Among the 449 college students returning at least one handedness questionnaire for their parents, a total of 449 fathers, 440 mothers, and 425 siblings participated in the study. The index of mixed-handedness (e.g., Degree of Handedness) showed highest heritability (0.67), followed by the Hand Preference Index (0.52), and then the Direction of Handedness (0.39). Using an index of mixed-handedness for future molecular studies was suggested.

Handedness and Physical Measures II: Objectively Measured Height and Weight

There is conflicting literature on the relationship between hand preference, height, and weight, with some research indicating increased height in non-right-handers, and others supporting both decreased height and decreased weight in this population. However, no previous research has objectively measured height and weight, examined a predominantly female population, or explicitly explored the contribution of handedness degree versus handedness direction in investigations. The present research objectively assessed height and weight in a sample of individuals with a range of hand preferences. Results: Left-handers were shorter than right-handers, but weighed the same. Left-handers therefore demonstrated a higher body mass index than right-handers. Conclusion: Results suggest handedness direction is related to objectively measure anthropomorphic characteristics in women. Because the current sample was predominantly female, future research could determine if the present findings reflect true gender differences in the relationship between height, weight, and handedness, or limitations of sample size.

Predictors of language lateralization in temporal lobe epilepsy

Among patients with epilepsy, atypical (rightward) language lateralization has been associated with left-handedness, a left seizure focus, an early age at seizure onset, and familial sinistrality, although these associations are not consistently observed. No study has examined all of these factors in relation to language lateralization in the same epilepsy sample, let alone in a sample comprised only of patients with temporal lobe epilepsy. Moreover, little consideration has been given in previous studies to how language lateralization might be influenced by the interplay between different factors, or how much unique variance in language lateralization is explained by each factor. The primary aim of this study was to examine the combined influences of handedness, side of seizure focus, age at seizure onset, and familial sinistrality on language lateralization in temporal lobe epilepsy patients. A secondary aim was to determine which factors uniquely contribute to the prediction of language lateralization. 162 patients with intractable temporal lobe epilepsy underwent functional MRI language mapping, from which language lateralization indexes were derived. Degree of handedness was measured via the Edinburgh Handedness Inventory. Main and 2-way interaction effects on language lateralization indexes were examined via linear regressions and Fisher exact tests. Significant effects were next examined in multiple regressions to identify unique predictors of language lateralization indexes. When examined in isolation in regressions, only left-handedness and a left seizure focus predicted atypical (rightward) language lateralization. These results, however, were qualified by interaction effects demonstrating that stronger left hand preference was associated with greater atypical language lateralization only among patients with a left seizure focus, an early or intermediate age at seizure onset, or no familial sinistrality. In follow-up multiple regressions, the interaction terms accounted for a significant amount of variance in language lateralization indexes above and beyond main effects. Additionally, side of seizure focus and its interaction with handedness uniquely predicted language lateralization indexes. Results indicate that degree of left-handedness is a marker of greater atypical (rightward) language lateralization in temporal lobe epilepsy but only in the context of seizure characteristics that have the potential to drive joint reorganization of language and hand preference (i.e., left seizure focus, or early or intermediate age at seizure onset) or in the absence of a genetic predisposition for left-handedness (i.e., no familial sinistrality). This study advances existing knowledge by illustrating how different factors combine to jointly affect language lateralization, and by identifying side of seizure focus and its interaction with handedness as unique predictors of language lateralization in temporal lobe epilepsy.

Handedness and effective connectivity of the motor system

Handedness denotes the individual predisposition to consistently use the left or right hand for most types of skilled movements. A putative neurobiological mechanism for handedness consists in hemisphere-specific differences in network dynamics that govern unimanual movements.We, therefore, used functional magnetic resonance imaging and dynamic causal modeling to investigate effective connectivity between key motor areas during fist closures of the dominant or non-dominant hand performed by 18 right- and 18 left-handers. Handedness was assessed employing the Edinburgh-Handedness-Inventory (EHI). The network of interest consisted of key motor regions in both hemispheres including the primary motor cortex (M1), supplementary motor area (SMA), ventral premotor cortex (PMv), motor putamen (Put) and motor cerebellum (Cb).The connectivity analysis revealed that in right-handed subjects movements of the dominant hand were associated with significantly stronger coupling of contralateral (left, i.e., dominant) SMA with ipsilateral SMA, ipsilateral PMv, contralateral motor putamen and contralateral M1 compared to equivalent connections in left-handers. The degree of handedness as indexed by the individual EHI scores also correlated with coupling parameters of these connections. In contrast, we found no differences between right- and left-handers when testing for the effect of movement speed on effective connectivity.In conclusion, the data show that handedness is associated with differences in effective connectivity within the human motor network with a prominent role of SMA in right-handers. Left-handers featured less asymmetry in effective connectivity implying different hemispheric mechanisms underlying hand motor control compared to right-handers.

Handedness predicts motivation to switch from the status quo

Degree of handedness is a correlate of structural brain asymmetries and predicts individual differences in episodic memory, belief updating and various biases in decision-making. We examined whether handedness moderated the status quo bias given previous research suggests that both constructs are related to loss aversion. Participants answered hypothetical scenarios in which they decided either to stay with the status quo or to switch. Results indicated that consistent and inconsistent right-handers both exhibited status quo bias (Experiment 1; N = 180), but inconsistent right-handers were more (or less) likely to stick with the status quo when informed of a positive (or negative) past experience. When provided with more equivocal information about the quality of the status quo and alternative, consistent-handers (CH) were more likely to show a status quo bias (Experiment 2; N = 222). Compared to CH, we argue that inconsistent-handers (IH) more readily update their beliefs in a manner consistent with how the status quo and alternative options are presented—switching when finding a reason to favour the alternative and staying when the status quo is described more favourably. These handedness differences fit a motivational account explaining status quo bias rather than a loss aversion account.

Does degree of handedness in a group of right-handed individuals affect language comprehension?

The impact of handedness on language processing has been studied extensively and the results indicate that there is a relationship between the two variables; however, the nature of the relationship is not at all clear. In the current study we explored degree of handedness (DH) opposed to direction in a group of right-handed individuals. fMRI was used to explore the impact of DH on the sentence comprehension network. The results revealed that during sentence comprehension activation in regions linked to semantic memory (e.g., anterior temporal cortex) were modulated by DH. Also, unexpectedly the precuneus/posterior cingulate gyrus which has been linked to episodic memory was also affected by DH. These results extend those reported previously by showing that the neural architecture that supports sentence comprehension is modulated by DH. More specifically, together the results presented here support the hypothesis proposed by Townsend, Carrithers, and Bever (2001) that DH interacts with the language system and impacts the strategy used during sentence comprehension.

Different association between intentionality competence and prefrontal volume in left- and right-handers

Intentionality is the ability to explain and predict the behaviour of others by attributing to them mental states, and is thus important for social cognition. Prefrontal cortex (PFC) including orbital and dorsal regions is implicated in a range of social and metacognitive executive functions (EFs). We investigate, for the first time, in 39 left-handers and 43 right-handers the effect of handedness on the relationship between intentionality and (i) PFC volume using stereology and (ii) grey matter (GM) volume within six a priori regions of interest using voxel-based morphometry (VBM). Although no association was found between degree of handedness and intentionality competence (p = .17), handedness groups differ significantly in the relationship between intentionality and PFC volume. Right-handers with handedness score =+75 (based on a range from −100 to +100) show a significant positive correlation between intentionality and orbital PFC volume (p = .01), while no significant correlation is observed for dorsal PFC volume (p = .82); and left-handers with handedness score =−75 show a significant positive correlation between intentionality and dorsal PFC volume (p = .02) while no significant correlation is observed for orbital PFC volume (p = .44). VBM results showed significantly greater GM volume correlated with intentionality in right-handers compared to left-handers (family-wise error – FWE, p < .05) in right temporo-parietal junction and superior temporal sulcus. Correlations between GM volume and intentionality were found across all subjects (FWE, p < .05) in bilateral middle frontal gyrus, superior temporal sulcus and right inferior frontal gyrus, superior frontal gyrus and precuneus. Overall, the findings suggest that the neuroanatomy underlying intentionality competence is influenced by handedness and that different methodological approaches can and should be considered in conjunction when investigating neuroanatomical correlates of psychological functioning.

Individual differences in information order effects: The importance of right-hemisphere access in belief updating

The order in which information is received alters the evaluation of causal hypotheses. Specifically, research suggests that the last piece of information oftentimes has the greatest impact on the evaluation and that the difference in subjective value between two pieces of information is an important factor influencing the magnitude of this recency effect. The present paper extends this line of work by exploring individual differences in this phenomenon via one's degree of handedness. Two hundred and five participants were given two hypothetical scenarios and related causal hypotheses accompanied by two pieces of additional information and asked to revise their belief in each hypothesis as information accumulated. Results confirmed predictions that 1) inconsistent/mixed-handers (those who use their non-dominant hand for at least some activities) show a larger effect with two pieces of inconsistent weak or strong information, and 2) neither mixed-handers nor consistent/strong-handers (those who use their dominant hand for almost all activities) show an effect with strong and weak pieces of consistent information. Mixed-handers' susceptibility to persuasive arguments and Ramachandran’s (1995; Ramachandran and Blakeslee, 1998) belief-updating theory centered around communication between the two halves of the brain and functional access to the right hemisphere are used to account for these data.

PCSK6 VNTR Polymorphism Is Associated with Degree of Handedness but Not Direction of Handedness

Although the left and right human cerebral hemispheres differ both functionally and anatomically, the mechanisms that underlie the establishment of these hemispheric specializations, as well as their physiological and behavioral implications, remain largely unknown. Since cerebral asymmetry is strongly correlated with handedness, and handedness is assumed to be influenced by a number of genetic and environmental factors, we performed an association study of LRRTM1 rs6733871 and a number of polymorphisms in PCSK6 and different aspects of handedness assessed with the Edinburgh handedness inventory in a sample of unrelated healthy adults (n = 1113). An intronic 33bp variable-number tandem repeat (VNTR) polymorphism in PCSK6 (rs10523972) shows a significant association (significance threshold: p<0.0025, adjusted for multiple comparisons) with a handedness category comparison (P = 0.0005) and degree of handedness (P = 0.001). These results provide further evidence for the role of PCSK6 as candidate for involvement in the biological mechanisms that underlie the establishment of normal brain lateralization and thus handedness and support the assumption that the degree of handedness, instead the direction, may be the more appropriate indicator of cerebral organization.

Laterality affects spontaneous recovery of contralateral hand motor function following motor cortex injury in rhesus monkeys

The purpose of this study was to test whether brain laterality influences spontaneous recovery of hand motor function after controlled brain injuries to arm areas of M1 and lateral premotor cortex (LPMC) of the hemisphere contralateral to the preferred hand in rhesus monkeys. We hypothesized that monkeys with stronger hand preference would exhibit poorer recovery of skilled hand use after such brain injury. Degree of handedness was assessed using a standard dexterity board task in which subjects could use either hand to retrieve small food pellets. Fine hand/digit motor function was assessed using a modified dexterity board before and after the M1 and LPMC lesions in ten monkeys. We found a strong negative relationship between the degree of handedness and the recovery of manipulation skill, demonstrating that higher hand preference was associated with poorer recovery of hand fine motor function. We also observed that monkeys with larger lesions within M1 and LPMC had greater initial impairment of manipulation and poorer recovery of reaching skill. We conclude that monkeys with a stronger hand preference are likely to show poorer recovery of contralesional hand fine motor skill after isolated brain lesions affecting the lateral frontal motor areas. These data may be extended to suggest that humans who exhibit weak hand dominance, and perhaps individuals who use both hands for fine motor tasks, may have a more favorable potential for recovery after a unilateral stroke or brain injury affecting the lateral cortical motor areas than individuals with a high degree of hand dominance.